Long-winged Harrier at El Real

aúl Arias also forwarded the following report by Allen Chartier. This would be the second Panama sighting of Long-winged Harrier:
While waiting for an airplane to arrive from La Palma to take us on a much-delayed flight to Panama City, a largish dark raptor flew low over the canegrass at the north (?) end of the runway about 30 yards away. As viewed through Zeiss 10 x 42 binoculars, the bird had an all-black head and underparts. The upper and under-wing coverts were all black as was the back. The face showed faintly, but clearly, a suggestion of facial disks (characteristic of harriers). The bill was dark and the color of the cere was not determined as it wasn’t particularly conspicuous. The remiges were checkered (or barred) with black and medium gray both above and below. The tail had 5-7 black bars with the same medium gray between. The rump and upper tail coverts were black except for a very narrow white edge on the distal upper tail coverts. The bird was shaped very much like a Northern Harrier, with very long narrow (but not tapered) wings and a long, narrow tail that was longer than the width of the wings. The wings were held in a distinct dihedral like a Turkey Vulture, but shallower. The legs were not seen.
Similar Species:
Zone-tailed Hawk, which has apparently been recorded from this precise location only once before (Ridgley in 1975) has broader wings, a shorter tail, white tail bands, dark remiges from above, has a prominent yellow cere, and lacks facial disks. Other dark raptors (Short-tailed Hawk, Hook-billed Kite, Great and Common Black-Hawks) are not shaped like this bird at all.
I am very familiar with Zone-tailed hawk, and the shape of this bird was very different. I am experienced in assessing the flight shapes and styles of flying raptors, as I have been a hawk counter and compiler for the Holiday Beach Migration Observatory since 1976.
I realize that this probably represents a first record for North America (A.O.U. area) and for Panama. I have seen Long-winged Harrier once before in the llanos of Venezuela.